1. Field of the Invention
The invention relates to a multiple-ratio geared transmission for an automotive vehicle with two gearsets arranged in series wherein ratio changes in the transmission are characterized by swap-shifts.
2. Background Art
A multiple-ratio power transmission mechanism with five forward driving ratios and a single reverse driving ratio is disclosed in U.S. Pat. No. 5,809,442, which is assigned to the assignee of the present invention. It includes a compound planetary gearset with three forward driving ratios, the gearing elements being arranged in a configuration that commonly is referred to as a compound planetary Simpson gearset. A second overdrive gearset is arranged in series with respect to the Simpson gearset and typically is located between the Simpson gearset and a hydrokinetic torque converter, which has an impeller driven by an internal combustion engine and a turbine connected drivably to a planetary carrier for the overdrive gearset. A ring gear of the overdrive gearset acts as a torque input element for the Simpson gearset.
The overdrive gearset is a simple planetary gearset, which establishes an overdrive ratio and a direct-drive ratio. It includes a friction brake for the reaction element and an overrunning coupling to establish torque flow between two elements of the overdrive gearset as the overdrive gearset is upshifted.
The Simpson gearset establishes three forward driving ratios. It includes a second overrunning coupling, which establishes a non-synchronous ratio shift. Forward drive is achieved by engaging a forward clutch during a shift from neutral to drive. A separate reverse engagement clutch is used to establish a torque flow path for reverse. Ratio changes are controlled by an electronic microprocessor, which develops signals in response to operating variables for the driveline of the vehicle to actuate and release shift solenoid valves, which in turn control shift valves.
On an upshift from the second ratio to the third ratio, reaction torque on one gear component is relieved as reaction torque for a companion gear component is applied. A 2-3 upshift involves a downshift of the overdrive gear unit while the Simpson gearset is upshifted. Both of these shifts are synchronized without losing capacity of the affected gear elements during the shift interval. This shift is referred to as a so-called “swap-shift.” In a similar fashion, a ratio change from the third ratio to the second ratio involves an upshift of the overdrive gear unit, while the Simpson gearset is downshifted.
U.S. Pat. No. 6,370,463 discloses a control system for controlling the timing of the application and release of the clutches and brakes during a swap-shift. The release of the reaction brake for the overdrive gearset and the application on the reaction brake for the Simpson gearset during an overall 2-3 upshift must be accomplished synchronously. An error in the synchronization would deteriorate the shift quality, which would be perceived by the vehicle operator as a shift shock due to inertia torque disturbances.
The control system reduces the capacity of the reaction brake for the overdrive gearset as the reaction brake for the Simpson gearset is increased. Early release of the friction brake for the overdrive gearset would cause a sudden increase in the torque transfer from the overdrive brake to the overrunning coupling, while the reaction brake for the Simpson gearset is still rotating. In a transmission of this kind, a torque transfer from the overdrive brake to the overrunning coupling of the overdrive gearset and an increase in the brake torque capacity for the Simpson gearset results in a large output torque spike if the brake application and release sequence is not precisely timed.